﻿namespace Letter.Net.Kcp.Library.FEC;

sealed class OutputInputByteTableCodingLoop : CodingLoopBase
{
    public override void codeSomeShards(
        byte[][] matrixRows,
        byte[][] inputs, int inputCount,
        byte[][] outputs, int outputCount,
        int offset, int byteCount)
    {
        byte[][] table = Galois.MULTIPLICATION_TABLE;
        for (int iOutput = 0; iOutput < outputCount; iOutput++)
        {
            byte[] outputShard = outputs[iOutput];
            byte[] matrixRow = matrixRows[iOutput];
            {
                int iInput = 0;
                byte[] inputShard = inputs[iInput];
                byte[] multTableRow = table[matrixRow[iInput]];
                for (int iByte = offset; iByte < offset + byteCount; iByte++)
                {
                    outputShard[iByte] = multTableRow[inputShard[iByte]];
                }
            }
            for (int iInput = 1; iInput < inputCount; iInput++)
            {
                byte[] inputShard = inputs[iInput];
                byte[] multTableRow = table[matrixRow[iInput] & 0xFF];
                for (int iByte = offset; iByte < offset + byteCount; iByte++)
                {
                    outputShard[iByte] ^= multTableRow[inputShard[iByte]];
                }
            }
        }
    }


    public override bool checkSomeShards(
        byte[][] matrixRows,
        byte[][] inputs, int inputCount,
        byte[][] toCheck, int checkCount,
        int offset, int byteCount,
        byte[] tempBuffer)
    {
        if (tempBuffer == null)
        {
            return base.checkSomeShards(matrixRows, inputs, inputCount, toCheck, checkCount, offset, byteCount,
                null);
        }

        byte[][] table = Galois.MULTIPLICATION_TABLE;
        for (int iOutput = 0; iOutput < checkCount; iOutput++)
        {
            byte[] outputShard = toCheck[iOutput];
            byte[] matrixRow = matrixRows[iOutput];
            {
                int iInput = 0;
                byte[] inputShard = inputs[iInput];
                byte[] multTableRow = table[matrixRow[iInput]];
                for (int iByte = offset; iByte < offset + byteCount; iByte++)
                {
                    tempBuffer[iByte] = multTableRow[inputShard[iByte]];
                }
            }
            for (int iInput = 1; iInput < inputCount; iInput++)
            {
                byte[] inputShard = inputs[iInput];
                byte[] multTableRow = table[matrixRow[iInput]];
                for (int iByte = offset; iByte < offset + byteCount; iByte++)
                {
                    tempBuffer[iByte] ^= multTableRow[inputShard[iByte]];
                }
            }

            for (int iByte = offset; iByte < offset + byteCount; iByte++)
            {
                if (tempBuffer[iByte] != outputShard[iByte])
                {
                    return false;
                }
            }
        }

        return true;
    }
}